The present invention relates to a contactless data processing apparatus which is used in the toll use of facilities or an apparatus or the like and, more particularly, to a contactless data processing apparatus for transmitting or receiving data in a contactless manner between a handcarried data carrier which a man carries and a fixed reader/writer.
Hitherto, as a data processing apparatus using a contactless data carrier which is used in the toll use of a ski lift, playing facilities, or the like and is known as what is called a data coin, for example, an apparatus as shown in FIG. 1 is known. In FIG. 1, reference numeral 100 denotes a reader/writer and numeral 200 indicates a data carrier. The reader/writer 100 is fixedly installed and has a control section 120, a read control section 140, a correlation arithmetic operating section 160, and a transmitting section 180. The data carrier 200 is carried by the user as, for example, a pendant or a wristwatch. The data carrier 200 has a non-volatile memory 300 such as an PROM or E.sup.2 PROM or the like, a control section 240, a pseudo random signal generating section 260, a transmitting section 280, a power supply circuit section 320, and a capacitor 340.
Such a data processing apparatus operates as follows. When the data carrier 200 is allowed to approach within a range of a distance where the reader/writer 100 can communicate, the supply of an operating electric power due to, for example, an electromagnetic inductive coupling from the transmitting section 180 of the reader/writer 100 is received by the transmitting section 280 of the data carrier 200. The received signal is rectified and smoothed by the power supply circuit section 320. A power source voltage V.sub.cc is charged into the capacitor 340, thereby making the data carrier operative. In this state, when the read control section 140 of the reader/writer 100 sends a read command to the data carrier 200, the command is decoded by the control section 240 of the data carrier 200 and data bits which are returned are sequentially supplied to the pseudo random signal generating section 260. Two kinds of pseudo random series signals which are used in correspondence to the data bits 1 and 0 have been preset in the pseudo random signal generating section 260. The generating section 260 generates either one of the pseudo random series signals corresponding to the data bit 0 or 1 and sends it from the transmitting section 280 to the reader/writer 100. The same pseudo random series signal as that in the data carrier 200 has been held as a reference signal in the correlation arithmetic operating section 160 of the reader/writer 100. An autocorrelation with the received signal is obtained. When the received signal coincides with the reference signal, an autocorrelation value increases like a peak, so that the reception of the bit 1 or 0 can be discriminated.
However, in such a data processing apparatus using the data carrier, since the contactless communicating system is used, an area in which the data carrier can access the reader/writer is also wide and the reader/writer can simultaneously communicate with two or more data carriers. Therefore, upon reading, read data from two or more data carriers is mixed and an error occurs. That is, when different data bits 0 and 1 are simultaneously transmitted from two data carriers, the data bit of the data carrier locating at the near distance is made effective. On the other hand, when the same data bit 0 or 1 is respectively transmitted from two data carriers, there is a problem in that the same data bit is received from two data carriers and data cannot be correctly read out.
The operating electric power, on the other hand, is supplied from the reader/writer 100 to the data carrier 200. Therefore, in the case where an arbitrary command is generated from the reader/writer 100 and the user tries to obtain a response by the pseudo random signal from the data carrier 200, there is a fear in that when the operating electric power of the data carrier 200 is lacking the electric power is instantaneously shut off during the returning operation of data using the pseudo random series signal.
Furthermore, since the data carrier is allowed to approach the reader/writer and the data is read by the operation of a man, a communicating distance during the transmission of data is not stable. Therefore, when the reading operation from the data carrier 200 is started, a predetermined command is generated and the pseudo random signal is returned. After confirming that the autocorrelation value is equal to or larger than a predetermined threshold value, the reading operation is started. By using such a method, an almost correct data bit can be read. However, even when the autocorrelation value obtained from the pseudo random signal which was returned prior to reading the data is equal to or larger than the threshold value, in the case where the data carrier 100 is away from the reader/writer 200 during the reading operation of the data from the data carrier 100, there is a possibility that the autocorrelation value decreases and the correct data bit cannot be read.